Secondary batteries are highly applicable to a variety of product groups and have electrical characteristics with high energy density. Such secondary batteries are applied not only to portable electronic devices but also to electric vehicles, hybrid vehicles, power storage devices and the like, driven by electric driving sources.
A battery pack applied to an electric vehicle or the like has a structure in which a plurality of battery modules, each having a plurality of battery cells, are connected to obtain high output. In addition, each battery cell is an electrode assembly which includes a positive electrode, a negative electrode current collector, a separator, an active material, an electrolyte and the like to allow repeated charging and discharging by an electrochemical reaction between components.
As the need for a large-capacity structure as an energy storage source has increased recently, there is a growing demand for a battery pack of a multi-module structure in which a plurality of secondary batteries connected in series or in parallel are grouped.
Meanwhile, the charging or discharging process of a secondary battery generates heat by electrochemical reactions. If the heat generated by the battery module during charging and discharging is not effectively removed, heat accumulation may occur. In this case, the battery may be degraded faster, and in some cases, fire or explosion may occur.